Suitability of static tests for acid rock drainage assessment of mine waste rock

Abstract

In the present study, eight rock samples were analysed with a modified acid-base accounting (ABA) test and the corresponding net acid generation (NAG) test. In addition, the main and trace elements solubilised during the tests were determined with ICPOES/MS. Both the modified ABA and NAG tests classified the rock samples with a low sulphide-S content (0.1-0.4%) and low carbonate mineral content (<0.2%) into the category of 'potentially acid generating'. The low neutralization potentials of these rocks were partly due to additional acid produced in silicate weathering, upon the hydrolyzation of Fe and Al during the tests. In contrast to the modified ABA, the contribution of slowly reactive carbonate minerals to the neutralisation potential was seen in the NAG test and in the carbonate NP calculation, as they classified the rock samples containing these minerals into the category of 'non-acid generating'. This supports the use of the carbonate neutralizing potential (NP) and/or the NAG test in mine waste screening. In the NAG test, acid generation and neutralization reactions either raising or decreasing the pH significantly influenced the solubility of trace metals and Al. This suggests that the extract contents could be useful in assessing contaminant mobility during long-term acid generating reactions.